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From YouTube: UKuG Yagi Antenna talk by Kent Britain WA5VJB
Description
UK Microwave Group (UKuG) member Kent Britain WA5VJB talks about 'Care and Feeding of Yagi’ Antennas' - including some interesting ways to doing Yagi’s and myths of Yagi Stacking.
- Recorded from the online UKuG talk on Wednesday 10 February 2021
A
We're
going
to
talk
about
driven
elements
and
yagi's
and
a
variety
of
things
that
people
think
are
true
about
yagi's.
Hopefully,
we'll
improve
a
variety
of
things
here.
This
is
the
optical
equivalent
of
a
yagi.
The
light
bulb
represents
the
driven
element.
We
have
a
mirror
in
back.
We
have
a
lens
in
front
and
electromagnetically
wave
wise.
This
is
the
same
thing.
A
The
yagi
is
doing
adding
another
reflector
doesn't
help,
but
we
can
add
more
lenses
and
change
the
focal
length
and
improve
the
gain
there
used
to
be
some
times
when
they
would
have
multiple
reflectors
on
the
yagi's.
You
will
know
virtually
all
the
modern
yagi's.
Don't
do
that
anymore.
Primarily,
that
was
correcting
other
issues
with
the
antenna.
A
Here's
something
I've
run
into
several
times
here
we
have
three
yagi's
one
has
what
I
would
call
a
normal
driven
element
in
the
middle
on
the
top
you'll
see
that
the
driven
element
is
longer
than
the
reflector.
Therefore,
all
the
waves
tend
to
go
around
the
reflector
and
go
out
the
back
of
the
antenna
down
at
the
bottom.
We
have
one
where
the
driven
element
is
shorter
than
the
first
director.
A
Therefore,
the
waves
can't
get
and
go
around
the
directors
and
that
just
doesn't
have
any
forward
game.
Yes,
I've
had
people
actually
tell
me
this.
In
reality,
the
driven
element
is
exciting.
The
yagi,
and
if
you
built
these
three
and
tested
them
on
the
antenna
range,
they
would
perform
identically.
A
A
A
We'll
start
with
the
good
old
driven
element,
impedance
70
ohms,
give
or
take
for
those
who
want
to
be
more
precise.
The
that
assumes
the
diameter
of
the
element
is
infinitesimal.
As
you
start
coming
into
more
realistic
diameters,
it
drops
down
a
little
bit,
but
70
ohms
give
or
take
here.
We
have
one
where
we
just
simply
have
two
dipole
elements:
two
reflectors
and
this
ends
up
being
a
nice
simple
dish
feed.
A
A
A
Here
we
show
if
you
have
72
ohms.
The
elements
are
going
to
be
much
further
apart.
If
I
have
a
high
impedance
300
ohm
line,
the
directors
have
to
be
very,
very
close
and
become
very
critical
in
both
spacing
and
length,
but
you
can
now
get
your
impedance
matching
with
the
physical
characteristics
of
the
yagi
itself.
Just
by
doing
your
spacing
properly.
A
Something
we're
starting
to
see
on
hf
antennas,
especially
the
multi-band
ones,
what
they
call
the
offset
fed
dipole.
If
I
feed
it
right
in
the
middle,
you
get
around
70
75
ohms,
as
I
start
moving
off
towards
the
edge
the
impedance
goes
up
in
theory.
If
I
had
it
exactly
from
the
edge
the
impedance
would
approach
infinity,
but
right
in
here
I
can
now
go
7500,
200
300.
Whatever
I
want
just
by
changing
the
spacing
here.
A
A
Schematic
represent
representation
of
the
gamma
match.
I
am
not
a
fan
of
the
gamma
match
for
a
whole
bunch
of
reasons
you
have
a
series
capacitor
and
inductor
tuning,
and
this
can
behave
as
an
antenna
tuning
element.
There
was
a
shall
we
say
popular
amsat
antenna
for
many
years
in
the
early
versions.
Not
today,
I've
been
working
with
tim,
the
early
versions.
A
A
A
I
don't
know
why
it
doesn't
like
that
photo.
Okay,
here
we'll
go
to
the
one
of
the
team
match
designs
again,
a
very
popular
one.
By
moving
the
shorting
elements,
I
can
get
any
impedance
ratio
that
I
want
again.
We
go
back
to
the
fridge
oven
and
you
can
see
where
you
actually
have
adjustment
screws
on
these
and
they
can
be
moved
in
and
out
on
your
sharding
bar
and
adjust
it
to
whatever
impedance
you
want.
A
This
is
a
design,
that's
becoming
more
and
more
popular
you're,
seeing
these
on
a
lot
of
stuff,
especially
the
ones
coming
out
of
asia.
The
coax
comes
up
through
the
bottom
of
the
driven
element
goes
around
the
inside
and
feeds
it
at
the
top
they're
actually
using
this
half
of
the
driven
element
as
the
balance.
A
A
A
A
You
have
one
driven
element
down
in
here
and
then
it
feeds
two
strings
of
directors.
So
now
I
have
stacked
yagi's,
but
no
power
divider.
The
antennas
themselves
are
taking
care
of
that.
I
think
this
has
some
potential
use
in
several
ham
applications,
especially
as
we
get
into
uhf
and
above,
but
most
of
the
computer
programs
do
not
deal
with
this
at
all
project
for
another
day.
A
Here's
an
example
of
one
for
a
european
uhf
television,
and
you
have
directors
tuned
to
three
different
frequencies
in
the
uhf
tv
band,
an
extremely
broad
band,
driven
element
and
then
a
reflector
which
hasn't
doesn't
have
any
particular
frequency.
Selectivity
certainly
has
some
possibilities
for
the
hand:
bands,
here's
one
that
chatted
with
the
guys
who
were
trying
to
improve
it
again,
you
have
your
directors
on
different
frequencies,
the
very
broadband
driven
element
and
they
were
trying
to
come
up
with
a
better
way
of
doing
the
driven
element.
A
A
A
A
The
discussion
was
regarding
the
stub
matching
that
he
was
using
here,
that
stub
radiates
off
to
the
sides
and
would
fill
in
the
side
nulls
of
the
antennas,
his
polar
his
computer
simulations
did
not
show
that
the
response
was
well
there's
no
current
in
that
stub.
Therefore,
I
don't
have
to
include
it
in
the
model.
A
A
A
A
Another
technique-
that's
used
quite
a
bit
in
the
past,
but
not
as
much
lately,
and
this
is
the
only
antenna
I've
seen
using
it
currently
is.
If
I
have
a
multi-band
beam,
I
can
take
the
driven
element,
especially
if
we're
working
with
a
two
meter
432,
which
is
third
harmonic,
and
I
can
drive
the
driven
element
as
a
half
wave
on
two
meters
or
as
a
wave
and
a
half
on
70
centimeters.
A
A
A
The
signal
comes
along
finds
the
elements
that
resonate
the
one
behind
it
is
longer,
so
it
acts
as
a
reflector.
The
one
in
fronts
are
shorter
and
act
like
directors,
so
a
log
periodic
is
basically
a
three
element,
yagi
on
a
very
large
number
of
frequencies
and
when
we'll
touch
on
aperture
area
in
a
moment
you
can
think
of
this
as
an
infinite
number
of
antennas,
all
sharing
the
same
aperture
area,
but
this
was
applied
to
yagi's.
A
A
In
reality,
we
now
know
that
the
variations
in
spacings
and
links
you
can
get
the
bandwidth
out
of
the
yagi.
The
driven
element
is
not
a
major
consideration
for
there,
and
this
is
a
dish.
That's
actually
part
of
the
tail
warning
the
radar
once
upon
a
time
out
of
a
b-29
and
a
little
pc
board,
log
periodic
feeding
it.
A
A
A
A
A
A
A
Gunther
dl6w
says
you
just
need
to
measure
it.
If
it's
this
important
and
his
suggestion,
was
you
build
a
three
element?
Yagi,
you
have
your
director
out
here,
supported
on
something,
that's
virtually
nothing.
A
small
piece
of
styrofoam
suspended
with
a
couple
of
bits
of
string
sitting
out
here,
but
you
know
the
distance
and
then
you
carefully
measure
the
swr
of
the
antenna.
A
Then
you
take
your
simulated
boom
element,
so
this
has
the
material
you
want
the
boom
material.
You
want.
The
keepers
you
want
and
you
put
it
in
exactly
the
same
place
then
adjust
its
length
until
you
get
exactly
the
same
swr
and
now
you
know
the
real
world
correction
factor
for
free
space
element
to
one
using
the
hardware.
You
want
to
use
and
there's
a
lot
of
speculations
out
there
as
to
what
that
correction
factor
should
be.
A
A
A
A
A
A
It's
just
not
used
commercially
very
often
because
it
just
doesn't
make
sense,
so
I
had
to
design
one
without
a
reflector.
Interestingly
the
computer
program.
Wouldn't
let
me
do
that,
but
I
made
the
reflecting
element
about
10
millimeters
long,
so
that
effectively
did
the
same
thing
and
the
computer
predicted
a
40
db
front
to
back
ratio
for
this
yagi.
A
A
A
A
A
A
A
A
A
Well,
does
it
screw
up
the
pattern?
Well,
we
need
to
measure
that
then.
So
here
is
a
470
centimeter
antenna
and
a
33
centimeter
antenna.
These
are
theoretically
first
and
second
harmonics
they're
harmonically
related.
So
I
started
looking
at
the
patterns.
Changing
the
spacing
between
them
got
down
pretty
close,
and
you
will
note
that
the
unused
antenna
has
a
50
ohm
load
on
it
and
continued
testing.
Until
I
reached
the
limit,
the
u-bolts
were
touching.
A
A
A
Oh
well,
whoops
forgot.
Yes,
I've
been
known
to
work
on
antennas
of
all
sizes.
These
are
some
550
meter
high
antennas,
not
far
from
my
house.
The
chap
on
the
left
is
a
director
of
engineering
for
a
network.
They
had
bought
a
station
here
that
had
problems
and
he
couldn't
get
anybody
working
for
him
to
come
there
and
help
him
make
some
measurements.
A
A
A
The
problem
with
the
b-29
was
you
had
two
bomb
bays
and
it
was
designed
to
carry
a
lot
of
little
bombs
and
the
ratchet
system
released
one
from
this
bombay
released.
One
from
this
released
one
from
this
released.
One
from
this
and
alternated
between
the
two
was
the
wing
spar,
so
they
couldn't
make
two
into
one
because
of
where
the
wing
spar
was.
A
A
A
A
A
B
Right,
thank
you,
kent.
That
was
an
interesting
talk
and
I
I'll
pass
it
over
to
john
in
a
moment,
because,
if
we've
got
questions
coming
in
I'll
john
will
read
them
out
to
you,
but
I've
got
one
one
question
for
you
myself.
Now
you
said
about
some
these
sort
of
problems,
with
corrosion
on
the
antennas
and
and
the
bit.
I
remember
you
saying
about
corrosion
between
the
the
the
elements
and
the
boom.
B
Now
I
think
virtually
all
the
amateur
yagi's
that
you
buy
have
got
the
the
boom
held
in
the
elements
held
in
some
way
other
than
being
welded
into
place.
So
what
what
would
you
suggest
would
be
the
the
best
way
of
actually
protecting
the
antenna?
Is
it?
Is
it
acceptable
to
sort
of
put
some
form
of
protective
coating
on
the
antenna
on
the
boom.
A
B
C
B
A
A
My
host
sam
jewell
has
one
up
and
I'm
tempted
to
try
to
acquire
one.
I
have
three
four
meter
stations.
I
have
a
couple
of
four
meter
antennas,
I'm
planning
to
put
them
up.
I
think
it
would
be
rather
interesting
to
point
jt,
65
or
jt8
back
at
the
uk
and
see
if
we
get
any
handling
in
this
particular
area
that
frequency
band
is
unused.
A
It's
what
we
call
white
space
and
I'm
chatting
with
brian
justin
who's,
the
only
person
I
know
who
has
a
four
meter
beacon
on
the
air
about
going
through
the
paperwork,
to
get
permission,
to
set
up
a
four
meter
station
so
next
summer,
when
he
has
an
f
layer
or
some
ease.
It
might
be
interesting
to
work
and
if
I
don't
get
the
license
I'll
just
mumble,
my
eight
g8
call
and
you'll
just
so
what
was
sacred
square
again.
A
A
C
A
A
Then
you
go
to
two
pieces
of
50
ohm
coax,
which
are
whatever
length
you
need,
but
the
same
when
I
built
my
eme
array,
the
phasing
lines
were
about
five
and
a
half
meters,
long
going
to
each
of
the
four
long
yagi's
and
using
just
a
simple
sweeper
and
dip
technique.
I
was
able
to
match
all
four
lines
to
within
one
centimeter.
A
A
B
Okay,
then,
if,
if
that's
all
the
questions,
we've
got
this
evening
just
looking
at
the
streaming
service-
and
I
don't
see
anything
else
coming
at
my
staff-
so
thank
you,
john
for
reading
those
out
and
I'd
like
to
thank
you
kent
for
a
very,
very
interesting
talk
tonight
and
and
that
interesting
little
bit
at
the
end
with
the
the
history.
I
don't
suppose
most
of
us
knew
knew
anything
about
about
that,
but
that
was
interesting.